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All About Fireflies

By Chris Williams on August 2, 2011.

Who hasn’t caught fireflies (or lightning bugs, if you prefer) as a child and placed them in a jar to watch their blinking display?

Fireflies are true beetles, not flies, although they are very soft-bodied compared to other beetles. The female lays her eggs in the ground where the developing larvae feed on worms and slugs, which they first paralyze. Adult fireflies usually feed on nectar or pollen, but some species are predators on other insects including other fireflies. An adult firefly lives for only a few days; just long enough to mate and reproduce.

The light show is produced when the firefly makes the chemicals luciferin and luciferase in its body. When oxygen is introduced into the beetle’s posterior end and combines with the chemicals, bioluminescence occurs. The light produced by a firefly is a cold light with very little heat.

The main reason for this light display is to attract a mate. At dusk, the male and female fireflies emerge from the grass. The male is the one flying just a few feet above the ground while the female climbs a blade of grass where she will flash when a male comes within 10-12 feet. The females of some species are wingless. There are over 170 different species of firefly in the U.S. and each has its own coded light pattern. The females of a species respond only to the particular pattern of the males of the same species (with one interesting exception which we will discuss later). She will then blink back the same intermittent code to the male who will then approach her for mating. Exchanges of signals are repeated 5 to 10 times until mating occurs. The warmer the weather, the faster the exchange of flashes.

It’s thought that another reason for the firefly’s light is to serve as a warning to predators of the beetle’s unappetizing taste. That makes sense because even the larvae of the firefly, called glow worms, produce bioluminescence and they’re not mating. A predator learns to associate the blinking light with a bad food choice, sparing the firefly.

But fireflies must taste okay to other fireflies because the females of some predatory species use the mating game to get dinner. By that I mean the male firefly is dinner. If a female can mimic the flashing pattern of another firefly species, she may get an unrelated male to land next to her where she will promptly eat him!

Needless to say, the amazing bioluminescence of the firefly has been heavily scrutinized by scientists. Their study of the firefly’s unique ability to produce cold light has contributed to the production of new flashlights and flares, among other things. In addition to its light capability, the luciferin and luciferase in the firefly’s body are used in research on cancer, multiple sclerosis, cystic fibrosis and heart disease.

There has been considerable concern recently among firefly lovers about the state of fireflies. People around the country were reporting an ongoing decline in the numbers of fireflies seen each summer. It’s thought the decline was largely due to a reduction in firefly habitat. But this year, firefly numbers seem to be on the increase again. That’s good news because it’s hard to imagine a world without fireflies!